The body displays a remarkable ability to maintain a relatively constant internal milieu when faced with increasing physical or psychological demands. A variety of autonomic and endocrine responses, coordinated in the CNS, serve to adapt the body to stress. In addition, the immune system plays an equal part in facing a variety of antigens. Increasing evidence has suggested that these three regulatory systems of the body are in constant communication. It is well established that glucocorticoids are elevated during an immune response and in turn inhibit the immune response. This feedback loop is thought to begin among immune cells that release a multitude of cytokines, including interleukin-1 (IL-1). IL-1 is a low molecular weight polypeptide that is believed to have endocrinologic, neurologic and immunologic functions. Within the CNS IL-1 is known to cause the release of corticotropin releasing factor (CRF) into the portal vessels, induce fever, cause anorexia, increase slow-wave sleep, increase central autonomic activity, etc. While the preoptic nucleus has been implicated as a site of action of IL-1 in inducing fever and CRF release, in general we do not know of the sites of action of IL-1 within the CNS. We now propose to study several aspects of IL-1 interactions with cells of the central CRF neuroendocrine system. The specific aims we will attempt to complete are: 1) To determine the distribution of activated neurons within the CNS following stimulation with IL-1beta. We will use a new neuroanatomic technique for functionally mapping the neurons activated by IL-1. This method involves immunocytochemical (ICC) localization of the Fos and Jun proteins which are rapidly and transiently expressed by neurons in response to physiological stimulation. The localization of the Fos and Jun proteins gives a picture of the pattern of synaptic activity. We will perform ICC for Fos and Jun and computerized morphometric analysis following the ip. or icv injection of IL-1beta. To determine if the activated cells project to CRF neurons, we will use a retrograde tracer to double label the Fos/Jun+ cells. To determine the transmitters used by the Fos/Jun+ neurons of the CNS, we will use double label ICC for Fos and/or Jun and TH, DBH, PNMT, CRF and AVP. 2) The second specific aim will be to localize the distribution of IL-1 receptors on cells of the central CRF system. Using in situ hybridization, we will localize those cells expressing IL-1 receptor mRNA that form the CRF system. Data from this method will then allow further studies on the regulation of the receptor within the CNS. 3) The 3rd specific aim is to determine the effect of IL-1 on the expression of CRF mRNA. These studies will involve both acute and chronic administration of IL-1 and in situ hybridization for CRF mRNA. 4) The final specific aim will be to determine the effect of IL-1 on the blood-brain barrier. Following both acute and chronic IL-1, the integrity of the blood-brain barrier will be determined using iv administration of horseradish peroxidase and localization at both the LM and EM levels. This information may have implications in our understanding of neural-endocrine- immune interactions and in CNS neuropathology.